The present patent application describes a new way to reduce the expansion of wood-plastic composites or more generally reduce the expansion of plastic composites containing cellulose particles. This unwanted expansion is caused by inevitable moisture absorption after production of these specific composite products. Wood plastic composites or more generally plastic composites containing cellulose particles normally are manufactured in a relatively dry state. This is necessary for obtaining a good product quality. After the manufacturing process these composite products will absorb moisture until an equilibrium state is reached. The uptake of moisture by the composite is accompanied by a dimensional expansion. This expansion can cause serious problems when it is restrained, or, alternatively may require unattractive large expansion gaps (dilatation gaps). Specially for applications of these composites in long profiles, e.g. for siding, decking, roof cladding or retaining walls the large expansion gaps (dilatations) that are necessary for allowing expansion create problems in the use of these materials. Sometimes expansion gaps are aesthetically unacceptable but also the necessity of expansion gaps may cause an unacceptable risk of forgetting them during installation. On the other hand, there is a need to make long profiles of these composites because these materials offer an optimum combination in terms of freedom in profile design, mechanical properties, durability, machineability, ease of installation and cost.                1. There is a need for profiles made of wood plastic composites or in general plastic composites containing cellulose particles.        2. There is a need for products as described in 1 that can be installed without expansion gaps.        3. There is a need for products as described in 2 without having future problems due to the expansion behavior of these products.        4. There is a need for products as described in 3 that can be machined with wood-working tools.        